Severe influenza infections can kill, particularly neonates and the elderly, but despite this little is known about the viral proteins involved in pathogenicity. In December Nature Medicine, Weisan Chen and colleagues from the National Institute of Allergy and Infectious Diseases, Bethesda, US, describe a novel influenza A virus mitochondrial protein that induces cell death in host immune cells sent to destroy the influenza virus.

Chen et al. searched for alternative peptides encoded by influenza A virus that are recognized by CD8⁺ cells and identified an abundant immunogenic peptide encoded by the +1 reading frame of the polymerase subunit PB1. Exposure of human monocytes to a synthetic version of PB1-F2 induced apoptosis. In addition, influenza viruses with targeted mutations that interfere with PB1-F2 expression induced less extensive apoptosis in human monocytic cells than those with intact PB1-F2 (Nat Med 2001, 7:1306-1312).

This protein could be an...